(1) Field of the Invention
The present invention relates to providing strain relief at the end of a potted wire, and deals more particularly with providing flexibility for the wire immediately adjacent to a potted length of fixed wire in an assembly that provides for flexing and bending of a movable portion of the same wire immediately adjacent to the potted portion.
(2) Description of the Prior Art
Elastomers such as polyurethanes are frequently used in potting applications because of their ease of casting and molding to particular shapes, and because of their ability to resist environmental containments such as water and oils. More specifically, in shipboard applications, such urethanes are frequently used to pot and to waterproof electrical connections. In spite of the use of soft urethane sleeves on flexible electrical conductor wires, failure often occurs at the junction site between the flexible portion of the wire and the hard junction formed by the relatively hard potting material used to secure the fixed portion of the wire. The potting compound comprises a hard urethane or epoxy and is generally contained in a metal barrel that protects other electronic components. The prior art approach to protecting the wire protruding from the barrel at this junction site is to provide a soft urethane sleeve around the wire portion adjacent to the hard potted fixed wire portion.
The above described prior art approach to protecting the junction between a flexible wire and a potted portion such as would be connected to an electrical component in a towed sonobuoy array has been used in towed arrays by U.S. Naval vessels. Such assemblies generally include a towed array having hinged places where the array is designed to fold consisting of wires and electronics potted in both a high durometer stiff urethane or epoxy inside a metal barrel, and a low durometer soft urethane outside of this barrel. During handling such subassemblies are subjected to bending at severe angles, repeated flexing, and abrupt changes in tensile loads. Such severe handling of these subassemblies takes it's toll on the wires where the wires emerge from the relatively hard or stiff potting material. Although the soft polyurethane material generally provided in this area has been thought to alleviate such bending there is little strain relief afforded to the flexible wire at the juncture between it and the relatively hard or stiff potting material. After what can sometimes be a relatively short period of time in service, mechanical fatigue and consequent electrical failure of this flexible wire can occur. This phenomena has been experimentally duplicated in the laboratory and these tests correlate well with actual test results at sea.
Morais, U.S. Pat. No. 4,992,629 discloses a cable shock absorbing apparatus in which a coil spring is mounted in a housing. The cable extends through the housing and has a loop portion within the housing that cooperates with the spring. When the cable is tensioned the housing sections telescope outwardly stretching the spring. Removing the tension relaxes the spring to telescope the housing sections inwardly.